This invention relates to internal combustion engines like those used in lawnmowers, snowblowers, generators and the like. More particularly, this invention relates to a dynamic gas seal that reduces the emissions of such engines.
In a typical prior art engine used on lawnmowers, snowblowers, generators and the like, a breather chamber is provided between the crankcase and the outside environment to prevent unwanted pressures from building within the crankcase. The breather also has a filter that removes much of the oil from the oil-laden crankcase air. The breather chamber is also in fluid flow communication with the intake valve system of the engine. The intake valve system includes the intake valve head, a valve stem, a valve guide that receives the valve stem, a return spring, and a cam for opening the valve. The air/fuel mixture from the carburetor or from another mixing device is received by the intake valve system and is drawn into the combustion chamber.
When the intake valve is open during partial load, the pressure difference between the intake valve and the breather chamber is very high. For example, the pressure at the valve head itself during partial load is typically on the order of -10 pounds per square inch (psi) during the intake stroke, while at the same time the pressure in the breather chamber is on the order of -1 to 0 psi. As a result, some of the oil-laden air and unburnt combustion gases pass from the breather chamber to the intake valve guide, and then through the intake valve into the combustion chamber. The oil-laden air is then oxidized in the cylinder, and is broken down into carbon and other components. The carbon tends to deposit on the exhaust valve face and on the cylinder wall. Exhaust emissions tend to increase when such carbon deposits form under the exhaust valve since the exhaust valve may no longer close completely during the intake and combustion strokes.
Also in the prior art system, the air laden with burnt gases is input upstream of the air/fuel mixing device; the result is that the mixing device erroneously makes the air/fuel mixture too rich since the device erroneously determines that the burnt gases contain air, when in fact the burnt gases are oxygen-deprived. Noxious emissions are thereby increased since the rich mixture is not completely burned during the combustion stroke.
One attempt to solve this problem was to use a labyrinth-type seal between the breather chamber and the intake valve system. However, such a seal is complicated and relatively expensive to manufacture.